1. Technical Field
The present disclosure relates to a multi-band antenna, in particular, to a multi-band antenna comprising a loop radiating portion disposed in a feeding portion.
2. Description of Related Art
Please refer to FIG. 1, which shows a schematic diagram illustrating a conventional multi-band antenna. The conventional multi-band antenna 1 comprises a radiating portion 16, a feeding portion 14, a shorting portion 15 and a parasitic monopole antenna 17. The radiating portion 16, the feeding portion 14 and the shorting portion 15 form a planar inverted F antenna. The radiating portion 16 is electrically connected to one end of the shorting portion 15 and one end of the feeding portion 14. Another end of the feeding portion 14 is electrically connected to a signal resource 13. Another end of the shorting portion 15 is electrically connected to a ground plate 12. One end of the parasitic monopole antenna 17 is an open end, and another end of the parasitic monopole antenna 17 is electrically connected to a ground plate 12.
The radiating portion 16 is divided into a first radiating portion 161 and a second radiating portion 162 by a connection point 16c which the feeding portion 14 is coupled to the radiating portion 16. The first radiating portion 161 is defined by one end 16a of the radiating portion 16 to the connection point 16c. The second radiating portion 162 is defined by another end 16b of the radiating portion 16 to the connection point 16c. The first radiating portion 161 is longer than the second radiating portion 162. The signal resource 13 operatively outputs at least one signal to the feeding portion 14, such that the first radiating portion 161 and the second radiating portion 162 respectively stimulate electromagnetic radiation signals with a first resonant frequency and a second resonant frequency. In addition, the first radiating portion 161 and the feeding portion 14 surround the parasitic monopole antenna 17, such that the electromagnetic radiation signal with the first resonant frequency couples to the parasitic monopole antenna 17. Accordingly, the parasitic monopole antenna 17 stimulates an electromagnetic radiation signal with a third resonant frequency, wherein the third resonant frequency is different with the first resonant frequency.
The conventional multi-band antenna 1 can be disposed in existing mobile devices and provides a multi-band operation achieving current requirements. However, the conventional multi-band antenna 1 has a problem in that the parasitic monopole antenna 17 is influenced by metal elements surrounding it, such that a stability of the conventional multi-band antenna 1 is also influenced when the conventional multi-band antenna 1 transmits or receives signals.